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How Worms Learn with PKD
The membrane-associated second messenger diacylglycerol (DAG), which is produced by phospholipase C (PLC) after its activation by various hormones and neurotransmitters, is known for its role in recruiting and activating various isoforms of protein kinase C (PKC). DAG also recruits and—with PKC—activates a family of kinases known as protein kinase D (PKD), which phosphorylate substrates distinct from those targeted by PKC. Although studies in cultured cells have suggested that PKD may regulate numerous cellular processes, its specific in vivo functions have remained unclear. Here, Fu et al. identify a previously unknown PKD isoform in the nematode Caenorhabditis elegans and show that this isoform, which they call DKF-2B, is found in neurons, unlike the previously identified DKF-2A isoform, which is mainly found in intestine. C. elegans learns to avoid Na+, normally a strong attractant, after being exposed to Na+-containing solutions in the absence of food. Experiments with various mutant and transgenic animals revealed that activation of neuronal and intestinal PKDs, by way of the PLC-DAG-PKC signaling pathway, was critical to the salt taste–induced learning.
